1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and apparatus for allocating a sounding channel in a wireless communication system.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16e standard was adopted in 2007 as a sixth standard for international mobile telecommunication (IMT)-2000 in the name of ‘WMAN-OFDMA TDD’ by the ITU-radio communication sector (ITU-R) which is one of sectors of the international telecommunication union (ITU). An IMT-advanced system has been prepared by the ITU-R as a next generation (i.e., 4th generation) mobile communication standard following the IMT-2000. It was determined by the IEEE 802.16 working group (WG) to conduct the 802.16m project for the purpose of creating an amendment standard of the existing IEEE 802.16e as a standard for the IMT-advanced system. As can be seen in the purpose above, the 802.16m standard has two aspects, that is, continuity from the past (i.e., the amendment of the existing 802.16e standard) and continuity to the future (i.e., the standard for the next generation IMT-advanced system). Therefore, the 802.16m standard needs to satisfy all requirements for the IMT-advanced system while maintaining compatibility with a mobile WiMAX system conforming to the 802.16e standard.
A control channel may be used to transmit various types of control signals for communication between a base station and a mobile station. An uplink control channel for the IEEE 802.16m system may include a fast feedback channel (FFBCH), a hybrid automatic repeat request (HARQ) feedback channel (HFBCH0, a sounding channel, a ranging channel, a bandwidth request channel (BRCH), and so on. Among uplink control channels of an IEEE 802.16m system, a sounding channel may be used by a base station (BS) to determine an uplink channel response for the purpose of an uplink closed-loop (CL) multiple-input multiple-output (MIMO) transmission and uplink scheduling. A terminal (or a mobile station (MS)) may transmit a sounding signal through a sounding channel, and the BS estimates a channel response based on the received sounding signal. In a time division duplex (TDD) system, the BS may use an estimated uplink channel response in order to perform a downlink (DL) CL MIMO transmission. Accordingly, a performance gain (or throughput), coverage, and link reliability can be enhanced.
Meanwhile, the IEEE 802.16m system has backward compatibility, so, it can support a terminal supporting an IEEE 802.16e system as well as a terminal supporting the IEEE 802.16m system. A case in which the IEEE 802.16m system supports a 802.16e terminal may be called a legacy support mode.
A method for effectively allocating a sounding channel in the legacy support mode is required.